The present invention relates to polygraphs, and more particularly to a polygraph with an improved cardiac monitoring channel.
Instruments for detecting and measuring physiological changes that accompany emotional stress are well known under the commonly used term of lie detectors. Such instruments are also often called polygraphs, and generally consist of sensors physically connected to an individuals body for measuring various physiological parameters. Standard sensors include a blood pressure cuff, a pair of respiration belts, and skin resistance finger electrodes, all suitably coupled to recording pins traversing a record chart. Examples of such instruments and polygraph measuring systems can be found in the following U.S. Pats:
______________________________________ U.S. Pat. No. Inventor Issue Date ______________________________________ 1,472,016 Dressler 10-23-23 2,235,894 Lee 03-25-41 2,655,425 Wood 10-13-53 2,944,542 Barnette et al 07-12-60 3,850,169 Gebben et al 11-26-74 3,908,641 Judson et al 09-30-75 3,915,156 Wastl et al 10-28-75 4,085,740 Allen, Jr. 04-25-78 4,178,918 Cornwell 12-18-79 4,219,028 Lencioni, Jr. 08-26-80 4,442,845 Stephens 04-17-84 4,520,232 Wilson 05-28-85 ______________________________________
When utilizing a polygraph for detecting deception, an examiner must be skilled in the ability to formulate appropriate questions which will cause a subject to physiologically react to those questions in order to indicate that the subject is not being truthful. In addition to the skill of the examiner, the polygraph or lie detector instrument must be able to detect these subtle changes in the state of the subject which accompany the physiological changes associated with the subject being untruthful. The above noted standard channels monitored by the lie detector instrument are traditionally considered to be under the control of the subject's autonomic nervous system and therefore not under the physical or conscious control of the subject. The basic idea is that when a subject becomes aroused by being asked questions the subject does not truthfully answer or questions which cause the subject to become aroused in general, the lie detection instrument will display changes in the noncontrollable physiologic parameters of the subject. The examiner can use these displayed changes to determine if the subject is aroused by the subject matter of the questions as an aid in detecting deception.
In a polygraph, the mechanical cardio channel has an ink pen over-shoot. The over-shoot of the ink pen of the mechanical cardio channel comes at the top of the blood pressure pulse, and is the result of the momentum of the mass of the ink pen which is produced during the reproduction of the rapid upstroke of the blood pressure pulse during a heart contraction. The ink pen, in the mechanical cardio channel, is directly connected to a blood pressure cuff which is wrapped around the upper arm of the subject. This blood pressure cuff is air inflated to couple the cuff to the brachial artery. When the heart contracts, it rapidly generates pressure which pumps or circulates blood to the body. This blood pressure pulse wave travels down the aorta, which is the main body artery, and is what is sensed by the blood pressure cuff around the subject's arm. The blood pressure wave has a characteristic periodic waveform which can be discussed in standard physiologic terminology. The waveform begins with an atrial contraction which is not always visible and which is usually seen in young people who have very elastic arteries and heart valves. Following the contraction of the atrium, the ventricles contract, pumping blood out of the heart to the lungs and general body circulation. The maximum pressure produced by the left ventricle is termed the systolic blood pressure and is represented by the peak of the blood pressure pulse waveform. Since the aorta is elastic, it is stretched by the blood being pumped from the left ventricle during contraction. Thereafter, the heart relaxes and blood pressure begins to fall. As the heart relaxes, blood is pushed back into the heart and out to the body by the stretched aorta. The entrance to the aorta has a one-way valve called the aortic valve which closes and stops blood from flowing back into the heart. The closing of this valve is what causes the dicrotic notch in the blood pressure pulse waveform. The diastolic run-off indicates the rate of blood flow out of the stretched aorta to the body. Finally, just before the beginning of the next heart beat, the blood pressure in the arteries drops to its lowest level which results in what is termed the diastolic blood pressure.
The ink pen over-shoot of the mechanical cardio channel, referred to above, is the result of the rapid pressure rise when the heart contracts. The rate of this pressure rise is an indication of the strength of contraction of the left ventricle. The strength of contraction of the left ventricle of the heart is determined by many things, such as (1) the strength of the heart muscle; (2) the heart rate; (3) the amount of blood that is in the left ventricle; (4) the resistance to the flow of blood in the body (the peripheral resistance); (5) the elasticity of the aorta; and (6) the state of excitation of the subject. These parameters are not under the conscious control of the subject, and for this reason, it would be desirable to obtain a measurement of the rate of blood pressure increase in order to provide an additional aid to an examiner for indicating deception by a polygraph subject.